In order to provide triboelectric chargeability, fluidity, and the like to a toner, an external additive such as silica has been used. However, when a toner detains in a developing machine due to continuous use of an electrophotographic apparatus or printer for a long period of time or the like, embedment of the external additive into the toner occurs due to a high shear and agitation for charging the toner. As a solution, although a method of adding the external additive in large quantity to the toner has been known, triboelectric chargeability and fluidity would change due to worsening of fixing ability, freeing of the external additive, and change of adhesion force and cohesion force of the toner. Regarding fixing ability, in a case where the external additive is increased, it is markedly worsened, and especially it is more severely affected in a non-contact heat-fixing. In addition, due to changes in triboelectric chargeability and fluidity, in a two-component developing system controlling the toner concentration in the developer using a magnetic permeability sensor, the toner concentration cannot be controlled to a given value, and lowering of the image density due to continuous printing, or the like becomes remarkable.
In addition, there has been disclosed a technique including the step of externally adding polytetrafluoroethylene as the external additive to the toner, thereby improving cleanability of the photoconductor and preventing melt-adhesion of the developer blade and the developer roller (see JP2000-305311 A and JP2003-114548 A). Further, there has been disclosed a technique including the step of adjusting charges of a toner having small particle size with polytetrafluoroethylene to prevent lowering of the image density (see JP-A-Hei-6-332231).